Why Bunkering Is One of the Highest-Risk Operations on Board
Bunkering is deceptively simple: fuel goes from supplier to ship.
In reality, it is one of the most hazardous, regulated, and commercially sensitive operations carried out during a vessel’s lifecycle.
A single bunkering or changeover failure can result in:
- Engine blackout
- Pollution incident
- Fire or explosion
- Off-hire, detention, or charterparty disputes
- Long-term machinery damage that appears weeks later
This article explains every major aspect of bunkering and fuel changeover, from equipment and methods to legal, operational, and human-factor risks—written for cadets through to Chief Engineers, Masters, ports, and shore-side technical staff.
This page sets the operational framework.
Detailed chemistry, purification theory, and injection behaviour are handled in later sections.
Table of Contents
- What Is Bunkering (Modern Definition)
- Where Bunkering Happens (Global Context)
- Types of Bunkering Operations
- Fuels Supplied During Bunkering
- Bunkering Equipment – Ship, Shore & Bunker Vessel
- Pre-Bunkering Planning & Risk Assessment
- The Bunkering Operation – Step by Step
- Sampling, Documentation & Disputes
- Fuel Changeover – Why It’s More Dangerous Than Bunkering
- Changeover Methods & Systems
- Common Failures & Blackout Scenarios
- Legal, Commercial & Regulatory Context
- Who Is Responsible – Ship, Supplier, Charterer
- How This Fits the Fuels Section
1. What Is Bunkering
Bunkering is the supply of fuel (“bunker”) to ships for propulsion and auxiliary machinery, including:
- Logistics
- Transfer
- Storage
- Measurement
- Documentation
- Initial onboard handling
The term originates from steamships, where coal was stored in bunkers. Today it refers almost exclusively to liquid and gaseous marine fuels.
A professional involved in buying and selling marine fuel is known as a bunker trader.
2. Where Bunkering Happens ?
Bunkering occurs:
- Alongside terminals
- At anchorages
- Offshore
- At sea (ship-to-ship)
Major Global Bunkering Hubs
- Port of Singapore
World’s largest bunkering port
2023 sales: ~51.8 million tonnes - Malta
Strategic STS bunkering hub (Hurd’s Bank) - Rotterdam, Fujairah, Houston, Zhoushan (regional hubs)
Ports are no longer just fuel suppliers—they are fuel strategy enablers for LNG, methanol, and future fuels.
3. Types of Bunkering Operations
3.1 Ship-to-Ship (STS) Bunkering
- Bunker barge alongside receiving vessel
- Most common method worldwide
- Flexible, high-volume capable
- Requires careful mooring, fendering, and communication
3.2 Port-to-Ship (PTS) / Terminal-to-Ship
- Pipeline from shore tank to vessel
- Very high transfer rates
- Typically used at major terminals
- Lower spill risk but less flexibility
3.3 Truck-to-Ship (TTS)
- Road tanker delivers fuel
- Common for small vessels, ports, inland waterways
- Limited volume
- High dependency on local regulations
3.4 Stern-Line Bunkering (SLB)
- Fuel transferred astern via hose
- Used in restricted anchorages
- Higher risk in poor weather
- Requires strict operational discipline
4. Fuels Supplied During Bunkering
Typical fuels bunkered:
- HFO / HSFO
- VLSFO
- MGO / DMA
- ULSFO
- LNG (cryogenic transfer)
- Methanol (increasingly common)
- Biofuel blends
Each fuel:
- Requires different transfer procedures
- Has different contamination risks
- Dictates changeover complexity
5. Bunkering Equipment – Ship, Shore & Bunker Vessel
Onboard Equipment
- Bunker manifolds (clearly marked)
- Drip trays & save-alls
- Bunker hoses / reducers
- Tank level gauging systems
- Overflow & vent arrangements
- Sounding pipes
- Emergency stop systems
Bunker Vessel / Shore Equipment
- Transfer pumps
- Flow meters / mass flow meters (MFM)
- Sampling points
- Emergency shutdown valves
- Spill containment gear
Equipment condition matters as much as procedures.
Many spills originate from gaskets, blanks, or hose failures.
6. Pre-Bunkering Planning & Risk Assessment
Before fuel transfer:
- Bunker checklist completed (ship & supplier)
- Quantities and grades confirmed
- Tanks designated and segregated
- Overflow paths verified
- Communication language agreed
- Emergency signals established
- Weather and traffic assessed
Key rule:
If you don’t know exactly where the fuel is going, do not start pumping.
7. The Bunkering Operation – Step by Step
- Manifold connection and pressure test
- Initial slow pumping (“line filling”)
- Tank changeover confirmation
- Increase to agreed rate
- Continuous monitoring:
- Tank levels
- Soundings
- Pump pressure
- Final topping-off at reduced rate
- Completion, draining, disconnection
- Hose blanking and cleanup
Human error during tank changeover is one of the most common spill causes.
8. Sampling, Documentation & Disputes
Sampling types:
- MARPOL sample
- Commercial sample
- Ship’s retained sample
- Supplier retained sample
Documents:
- Bunker Delivery Note (BDN)
- Time logs
- Meter readings
- Seal numbers
Fuel disputes often hinge on:
- Incorrect sampling location
- Poor sealing
- Missing timestamps
- Incomplete logs
9. Fuel Changeover – Why It’s More Dangerous Than Bunkering
Changeover is where most blackouts occur.
Risks include:
- Viscosity mismatch
- Thermal shock
- Wax precipitation
- Fuel pump seizure
- Injector sticking
- Air ingress
Changeover is not a paperwork task—it is an engine operation.
10. Changeover Methods & Systems
Manual Changeover
- Operator controlled
- High awareness required
- Common on older vessels
Automated Changeover Systems
- Temperature-controlled blending
- Flow-regulated transition
- Alarm-driven safeguards
Critical parameters:
- Temperature gradient
- Viscosity at engine inlet
- Fuel pressure stability
- Return fuel routing
11. Common Failures & Blackout Scenarios
- Switching to cold MGO too quickly
- Mixing incompatible VLSFO batches
- Air drawn during tank depletion
- Wax dropout in cold climates
- Incorrect valve lineup
Many blackouts occur hours after changeover, not immediately.
12. Legal, Commercial & Regulatory Context
Bunkering is embedded in maritime law:
- Charterparty obligations
- Seaworthiness requirements
- Deviation rules
- Insurance coverage
Regulation driven by International Maritime Organization through:
- MARPOL Annex VI
- IMO 2020
Running out of fuel or non-compliant bunkering can:
- Void insurance
- Trigger off-hire
- Lead to detention or salvage claims
13. Who Is Responsible?
| Party | Responsibility |
| Supplier | Fuel supplied to spec |
| Ship | Safe transfer & handling |
| Charterer | Fuel selection (often) |
| Master | Overall safety |
| Chief Engineer | Technical execution |
| Port | Environmental compliance |
Responsibility overlaps—but failure is rarely shared equally.
14. How This Fits the Fuels Section
This article connects directly to:
- Storage, Heating & Transfer → system design
- Purification & Treatment → post-bunkering defence
- Fuel Injection Systems → consequences of bad changeover
- Faults & Troubleshooting → blackout analysis
- Environmental & MARPOL VI → compliance enforcement
Key Takeaway
In the simpliest of terms bunkering puts fuel on board.
Changeover decides whether the ship survives it.